linux-kernel - Re: [Patch V2 4/4] ARM: dts: AM33XX: update rtc node compatibility

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Message-ID: <20130802112018.GI2884@e106331-lin.cambridge.arm.com>
Date:	Fri, 2 Aug 2013 12:20:18 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Gururaja Hebbar <gururaja.hebbar@...com>
Cc:	"davinci-linux-open-source@...ux.davincidsp.com" 
	<davinci-linux-open-source@...ux.davincidsp.com>,
	"tony@...mide.com" <tony@...mide.com>,
	"benoit.cousson@...il.com" <benoit.cousson@...il.com>,
	Sekhar Nori <nsekhar@...com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"vaibhav.bedia@...com" <vaibhav.bedia@...com>,
	"benoit.cousson@...aro.org" <benoit.cousson@...aro.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [Patch V2 4/4] ARM: dts: AM33XX: update rtc node compatibility

On Fri, Aug 02, 2013 at 12:07:36PM +0100, Gururaja Hebbar wrote:
> On 8/1/2013 10:35 PM, Mark Rutland wrote:
> > On Tue, Jul 30, 2013 at 05:21:14PM +0100, Sekhar Nori wrote:
> >> On 7/30/2013 8:25 PM, Mark Rutland wrote:
> >>> On Tue, Jul 30, 2013 at 06:05:52AM +0100, Gururaja Hebbar wrote:
> >>>> Hi,
> >>>>
> >>>> On 7/3/2013 2:17 PM, Hebbar Gururaja wrote:
> >>>>> Since AM33xx  RTC IP has RTC_IRQWAKEEN to support Alarm Wake-up.
> >>>>>
> >>>>> Update the rtc compatible property to "ti,am3352-rtc" to enable handling
> >>>>> of this feature inside rtc-omap driver.
> >>>>
> >>>> The other 2 rtc driver related patches have been pulled up. If you have
> >>>> no comments, can you please pull this up.
> >>>>
> >>>> Regards
> >>>> Gururaja
> >>>>
> >>>>>
> >>>>> Signed-off-by: Hebbar Gururaja <gururaja.hebbar@...com>
> >>>>> ---
> >>>>> :100644 100644 77aa1b0... dde180a... M	arch/arm/boot/dts/am33xx.dtsi
> >>>>>    arch/arm/boot/dts/am33xx.dtsi |    2 +-
> >>>>>    1 file changed, 1 insertion(+), 1 deletion(-)
> >>>>>
> >>>>> diff --git a/arch/arm/boot/dts/am33xx.dtsi b/arch/arm/boot/dts/am33xx.dtsi
> >>>>> index 77aa1b0..dde180a 100644
> >>>>> --- a/arch/arm/boot/dts/am33xx.dtsi
> >>>>> +++ b/arch/arm/boot/dts/am33xx.dtsi
> >>>>> @@ -297,7 +297,7 @@
> >>>>>    		};
> >>>>>
> >>>>>    		rtc@...3e000 {
> >>>>> -			compatible = "ti,da830-rtc";
> >>>>> +			compatible = "ti,am3352-rtc";
> >>>
> >>> Given that this is backwards compatible with the old binding, it would
> >>> be nicer to have this as:
> >>>
> >>> 	compatible = "ti,am3352-rtc", "ti,da830-rtc";
> >>>
> >>> We must get into the habit of changing dts files in a
> >>> backwards-compatible fashion.
> >>
> >> Right, I suggested this when v1 was posted. It turns out the current
> >> kernel does not handle the compatilble list correctly and the string
> >> selected actually depends on the order in which it appears in match
> >> table in driver instead.
> >>
> >> I saw there were patches being discussed to fix this issue, but until
> >> that is fixed, we cannot really use what you (and I before) suggested.
> >
> > A temporary solution would be to list the "ti,am3352-rtc" first in the
> > of_match_table kernel-side.
> 
> If above method is followed, then it would cause trouble on davinci 
> platform because this rtc-omap driver is also used by Davinci platform.
> On davinci Plaform the driver would match with "ti,am3352-rtc" for 
> compatible.

Sorry, I don't follow. Does the davinci dt have "ti,am3352-rtc" in it's
compatible string list?

If so, and it's not compatible, the dts is wrong.

If not, then we won't use the behaviour specific to "ti,am3352-rtc", and
there's no problem.

What trouble would this cause?

Thanks,
Mark.

> 
> Regards
> Gururaja
> 
> > That way you can keep the old compatible
> > string in the dts compatible list, and maintain backwards compatibilty
> > with older kernels.
> >
> > Later if the way Linux matches compatible strings is changed, this
> > shouldn't break the probe order, and the of_match_table order could be
> > changed.
> >
> > Have I missed something?
> >
> > Thanks,
> > Mark.
> >
> 
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
> 
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